Inductors are used in circuits to help regulate current flow through the circuit. When a current flows through the inductor, energy is stored temporarily in a magnetic field in the inductor. When the current flowing through the inductor changes, a time-varying magnetic field within the inductor induces a voltage in the inductor which opposes the change in current that created the magnetic field.
A transformer is a static electrical device that transfers energy by inductive coupling between winding circuits. A varying current in a primary winding creates a varying magnetic flux in a core of the transformer and varies a magnetic flux through a secondary winding. The varying magnetic flux induces a varying voltage in the secondary winding.
As technology nodes shrink, circuit sizes are reduced. Inductors or transformers occupy a large area in a circuit design. As the circuit size decreases, proximity between the inductor or transformer and the other devices increases. Further, as metal lines in these components decrease in size, a resistance in the metal lines increases. The increased resistance in turn lowers the quality (Q) factor of the inductors and transformers. In addition, inductors and transformers cause a magnetic flux to pass through the circuit. The magnetic flux is capable of introducing noise into other devices within the circuit.